Electric discharge tube



June 22 1926. 1,589,905

J. M. SCHMIERER ELECTRIC DISCHARGE TUBE Filed Sept. 1 1921 Patented June 22, 1926.

UNITED STATES PATENT OFFICE.

ELECTRIC DISCHARGE TUBE.

Application filed September 1, 1921, Serial No. 497,576, and in Germany April 30, 1920.

This invention relates to luminous electric discharge lamps or tubes, sometimes referred to as glow lamps, in which the gaseous filling within a glass or other transparent envelope becomes luminescent upon the passage of an electric discharge between electrodes contained within the envelope.

The object of the invention is to produce a glow lamp in which a large amount of luminescence is obtainable and which will operate on relatively low voltage.

In order to obtain the desired increased luminescence, it is necessary to have a long discharge path between the electrodes, but ieretofore in so far as it has been possible to ascertain, it has not been possible to accomplish this end with low voltages.

The present invention takes advantage of a certain characteristic referred to herein as cathode drop which differs widelyin the different metals which may be utilized as cathode elements. In a discharge lamp of the kind herein dealt with the luminescence is of two kinds, known, respectively, as negative luminescence and positive luminescence, the former being situated adjacent the oathode and the latter adjacent the anode. The term cathode drop as herein used, meanssubstantially the potential drop between the negative luminescent layer and the cathode. The cathode drop depends, not entirely upon the metal used, as a cathode element, but also upon the gas filling and the gas pressure. It is lowest with the alkali metals, rare gases and gas pressures of 3 to 12 millimeters mercury columns. It is highest with the noble metals, common gases and gas pressures of more than 15 and less than 3 millimeters mercury columns.

The metals which may be used advan-- tageously for cathodes in accordance with the present invention are copper, iron, aluminum and the alkali metals, sodium and potassium. Of these metals, copper is characterized by the highest cathode drop, next comes iron, then aluminum, followed by the alkali metals.

If the cathode of a glow lamp is made of a metal characterized by low cathode drop and is disposed closely enough to the anode so that the lamp will operate on comparatively low voltage, say for example 220 volts, the length of the discharge is quite short because the electrodes are of necessity placed quite closely together. With the same spac ing between the electrodes, and the cathodes made of metal having a higher cathode drop, ihe voltage required to start and operate the lamp is materially increased.

By the present invention a long discharge path is obtained in a glow lamp operable on relatively low voltage, such as 220 volts. This is accomplished by the provision of a cathode made up of two or more different metals characterized by difierent cathode drops. The cathode is so constructed that the portion of it which is made of metal of the highest cathode drop is disposed nearest the anode. The other portions of the cathode are disposed, respectively, further away from the anode in theinverse order of their cathode drop. In other words, the exposed surface of the metal, having the lowest cathode drop is situated the greatest distance from the anode. Since the portion of highest cathode drop is situated nearest the anode, it is necessary that the electrodes be placed more closely together than would be necessary if the cathode were made entirely of a metal of low cathode drop. But this is immaterial since with a cathode of the construction herein described, the luminescent.

electrical discharge which first occurs only between the anode and the end of the cathode nearest the anode, spreads immediately to the portion of the cathode of lower cathode drop and thence to the portion of still lower cathode drop, providing there are more than two portions. The result is a long column of positive luminescence, together with a short column or layer of negative luminescence near the cathode. The explanation of this phenomenon is that the total resistance of the non-ionized gas-filled space between the two electrodes determines the necessary starting voltage, Whereas, after the discharge has started the cathode drop is the main factor in determining the voltage required. Since the starting resistance is least across the shortest space between anode and cathode the initial discharge will occur across that space, but having once reached up into the neighborhood of the next successive portion of the cathode, having a lower cathode drop, a greater portion of the discharge will occur between the latter portion and the anode. For the same reason the discharge will creep up to the next successive portion of the cathode.

In the accompanying drawing there is illustrated a glow lamp in accordance with this invention, wherein, 1 is a glass envelope containing a gaseous filling. Two electrodes are shown enclosed within the glass envelope. These are an anode 2, which may be of. copper, and acathode comprising three portions, 3, 4 and 5, respectively. The portion 3 which is disposed nearest the anode may consist of a metal such as copper, having a relatively high cathode drop. The next succeeding portion may be made of a metal such as aluminum having a lower cathode drop, while the next succeeding por tion, 5, may be conveniently made of one of the alkali metals, sodium or potassium, having a still lower cathode drop. The method of securing the three portions of the cathode together is relatively immaterial. The cathode structure is, in fact, so simple that it will be perfectly apparent to anyone skilled in the art how it may be made in ractice.

The two electrodes are provided with leading-in conductors to which a suitable current source may be connected.

The space between the anode 2 and portion 3 of the cathode may be established so that an initial discharge will occur at the voltage at which the lamp is expected to opcrate. The first luminescence after switching on the current occurs only between the anode and the portion 3, but the discharge immediately creeps up to the portion 4 of the cathode, having a lower cathode drop and then up to the portion 5 having a still lower cathode drop. \Vith the exception of a narrow layer of negative luminescence near the portion 5 of the cathode, the remaining space within the lamp, between the anode and the portion 5 is filled with positive luminescence.

The lamp shown in the drawing is intended more particularly to operate on direct current. For alternating current operation the two electrodes may be made the same as the cathode in the lamp shown in which case each electrode will become alternately anode and cathode.

This invention is capable of embodiment in a wide variety of forms and should not be construed as limited except by the scope of the appended claims.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare what I claim is:

1. A glow lamp comprising a pair of cooperative electrodcs, one ofsaid electrodes consisting of a plurality of conducting sec tions of substantially different cathode drop characteristics, the section of said last men tioned electrode disposed nearest the other of said electrodes being conductive at ordinary temperatures and characterized by relatively high cathode drop and the succeeding section or sections being characterized by successively lower cathode drop.

2. In a glow lamp, an anode and a cathode, in cooperative relation, said cathode comprising a plurality of adjoining sections of conductive material, the section of said cathode nearest said anode being conductive at ordinary temperatures and characterized by relatively high cathode drop, and the adjoining section of said cathode being characterized by substantially lower cathode drop.

3. In a glow lamp, a pair of cooperative electrode elements, one of said elements comprising a series of adjoining sections of conductive material of successively decreasing cathode drop, the section of highest cathode drop being disposed nearest the other electrode element and the remaining section or sections being disposed at successively greater distances from said other electrode element in inverse order to their relative cathode drop, the exposed surface areas of said sections being of different dimensions inversely as their relative cathode drop characteristics, said section of highest cathode drop being conductive at ordinary temperatures.

In testimony whereof I aifix my signature.

JOHANNES MICHAEL SCHMIERER. 

